1. Technical Field
The invention generally relates to a line replaceable unit and more specifically to a line replaceable unit that has a universal heat sink receptacle for receiving heat spreaders of different types of computer-on-module boards.
2. Related Technology
Line replaceable units (LRUs) are electronic modules that are designed to be replaced or swapped as a unit. Each LRU may include multiple electronic systems. However, each LRU is essentially self contained and configured to be replaced as a unit. LRUs are commonly used in aviation and other transportation industries. For example an aircraft may utilize multiple LRUs, each LRU including electronic components for one or more aircraft systems, such as navigation, communication, pressurization, etc. When a malfunction is detected in a system, maintenance personnel locate the affected LRU containing the suspect components and, once located, the malfunctioning LRU is replaced with a new LRU. Because the LRUs are essentially self contained, swapping a malfunctioning LRU for a new LRU is very efficient, sometimes taking only minutes to complete. As a result, LRUs enhance maintenance reliability for aircraft or other vehicle operations.
LRUs are designed to specifications to assure that they can be interchanged, especially if they are from different manufacturers. Usually a class of LRUs will have coordinated environmental specifications (i.e. temperature, condensation, etc.). However, each particular LRU may also have detailed specifications describing its function, tray size, tray connectors, attachment points, weight ranges, etc. It is common for LRU trays to have connections for rapid mounting, cooling air, power and grounding. The mounting hardware is often manually-removable, standard screw-detent quick-release fittings. Front-mounted electrical connectors are often jacks for ring-locked cannon plugs that can be removed and replaced without tools. Specifications also may define the supporting tools necessary to remove and replace the unit. Many LRUs require no tools for removal and replacement. Most LRUs also have handles, and specific requirements for their bulk and weight. LRUs typically need to be “transportable” and to fit through doors or hatches. There are also requirements for resistance to flammability, limits on unwanted radio emissions, resistance to damage from fungus, limited static electricity emissions, heat limits, pressure limits, humidity limits, condensation drip limits, vibration limits, radiation limits and other environmental factor limits.
LRUs may include one or more computer-on-module (COM) components or boards. A computer-on-module component is a highly integrated and compact PC that may be used in a design application much like an integrated circuit component. Each COM module may integrate core CPU and memory functionality, the common I/O of a PC/AT, USB, audio, graphics (PEG), and/or Ethernet. I/O signals are mapped to two high density, low profile connectors on the bottom side of the module. COM modules are used in LRUs to produce desired functionality for different systems. One type of COM module that is extensively used in aviation LRUs is the COM Express® module. Com Express is a specification hosted by PCI International Computer Manufacturer's group, a consortium computer manufacturing companies.
Generally speaking, COM Express modules have 7 pin out configurations and 4 different module sizes that are based on industry standard specifications. Thus, while having industry standard characteristics, COM Express modules may have different physical layouts. Because COM Express modules are electronic components, they generate heat that must be removed from the COM Express module so that COM Express module is not damaged. Generally, heat is removed from COM Express modules in LRUs by gas convection. More specifically, gas, usually ambient air, is circulated within the LRU and around COM Express module components. This circulating gas removes heat from the COM Express module through convection. While effective, the gas convection systems require a fan or other component to actively move the gas around the COM Express module, which adds weight and complexity to these systems. While heat sinks have been used to remove heat from COM Express modules, these heat sinks have been customized to each individual COM Express module because COM Express modules have different physical configurations or form factors. These customized heat sinks require more custom LRU side panels to be carried in inventory, to accommodate the custom COM Express heat sink form factors, which limits redesign or reconfiguration flexibility of the LRUs themselves.